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|Title:||Theoretical study of surface related phenomena of BCC transition metals|
|Doctoral Committee Chair(s):||Adams, James B.|
|Department / Program:||Materials Science and Engineering|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Physics, Condensed Matter
Engineering, Materials Science
|Abstract:||We have carried out a theoretical study of surface related phenomena for three bcc transition metals: tungsten (W), molybdenum (Mo) and vanadium (V), using a newly developed atomic potential, the fourth moment method. The fourth moment method is based on the second, third and fourth moment approximation of tight-binding theory in which three and four body terms are included to describe the partially filled d-bands. This method was fit to twelve bulk properties and the fitting results of these bulk properties are in good agreement with experimental results, except for some phonon modes.
This potential was used to study surface related phenomena. (1) Structure of W(100), Mo(100), V(100), W(110), W(111), W(210), W(211), W(310) and W(321) surfaces. (2) Self-diffusion of W single adatoms on the W(110), (211) and (321) surfaces. The binding site, the activation energy and pre-exponential factor of single W adatom diffusion on these surfaces have been calculated. (3) Small cluster interaction on W(110). The present calculations indicate a strong angular anisotropy and oscillatory behavior of W adatom-adatom interactions on W(110). For long ranges, the interaction is slightly repulsive. (4) Small cluster diffusion on W(110) and (211). We studied the diffusion mechanism of W dimer on those surfaces. The activation energy barrier and pre-exponential factor for W dimer migration have been determined.
In general, most of the calculations are in good agreement with experimental results and ab initio calculations. Some of our results are for systems not previously studied. These calculations have resulted in a more detailed understanding of surface structure and diffusion mechanisms on those surfaces. We found that the inclusion of angular terms does significantly improve the description of the bcc transition metals. This potential is a significant improvement over previous empirical models.
|Rights Information:||Copyright 1995 Xu, Wei|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9543777|
This item appears in the following Collection(s)
Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois
Dissertations and Theses - Materials Science and Engineering